1. Field of the Invention
The present invention relates to a video signal correction apparatus for improving image quality by compensating for color bleeding in video devices such as video cassette recorders, video cameras, full-color image printers, and full-color facsimile machines used to manipulate color pictures, and in data devices for storing image information on magnetic disks, optical disks, and other media.
2. Description of the Prior Art
With the development of full-color hard copy output technologies in recent years, it is quickly becoming possible to faithfully reproduce original images using such printing technologies as subliminal thermal transfer. This capability is, in turn, accelerating demand for hard-copy still image output. The development of high definition television (HDTV) and other high resolution video signal technologies, color reproduction capabilities are also now nearly comparable to traditional silver halide photographic capabilities.
When outputting hard-copy still images of current television signal formats (e.g., NTSC signals), however, the image resolution is limited by the limited bandwidth of the video signal. The resolution of the color difference signal in particular is less than 1/3 that of the luminance signal. As a result, images in which there should be a color change due to a change in luminance are recorded using the color before the luminance change after the luminance changes because the change in the color difference value cannot keep pace with the change in luminance. Simply stated, images with much color bleeding are often recorded.
A method of removing this color bleeding by adding edge information from the luminance signal to the color difference signal has been proposed in Japanese patent laid-open No. 2-213282. This reference fails to teach the color bleeding correction by the use of color difference signal.
FIG. 26 is a block diagram of a conventional video signal correction apparatus for correcting color bleeding. Referring to FIG. 26, the luminance signal Y and color difference signals R-Y, B-Y output from the digital signal source 100 pass through the interface 101 and are stored in the image memory 102. The edge correction circuit 103 performs the digital processing for both vertical and horizontal aperture correction based on the luminance signal read from the image memory 102.
After edge blurring is corrected by the edge correction circuit 103, the luminance signal is output to the digital signal processor (DSP) 106, and the edge correction component is output as edge information to the adder 105. The noise component of the color difference signals R-Y, B-Y read from the image memory 102 is then reduced by the low-pass filter (LPF) 104, the edge information from the edge correction component of the luminance signal is then added by adders 105A and 105B, and the result is output to the DSP 106.
Saturation enhancement, gamma correction, and other image enhancements based on the input luminance signal and color difference signals R-Y, B-Y are applied by the DSP 106 before the digital signal is output to the printer 109. When one frame comprises two fields as in the NTSC signal format, a motion detection circuit 107 is provided between the interface 101 and image memory 102 for removal of image motion between the first and second fields. A scan line correction circuit 108 for extracting the frame image from the fields is connected to the motion detection circuit 107. The printer 109 prints the image to the desired paper or other medium based on the output signal from the DSP 106.
With this configuration, however, when the bandwidth of the color difference signal is significantly narrower than the luminance signal bandwidth as in the NTSC format, adding the edge correction component of the luminance signal to the color difference signals does not significantly correct color difference signal bleeding. In fact, image areas of differing colors occur at the edge correction area of the luminance signal, resulting in further deterioration of image quality. In addition, pseudo-edges (ghosting) can easily occur because the edge correction component is added even where the color difference signal value is constant.